I just saw a commercial for aojiru, which appeared
to be some sort of green health drink.

Going to www.aojiru.com just brought up some
incomprehensible Japanese web site.

Ah! Wikipedia has it!

http://en.wikipedia.org/wiki/Aojiru

I especially like this description:

The taste of aojiru is famously unpleasant, so much
so that drinking a glass of the liquid is a common
punishment on Japanese TV game shows.